1. Field of the Invention
This invention relates to an air hardening steel. This invention also relates to an air hardening cast steel having a reduced nickel content and an acceptable impact toughness level.
2. Description of Related Art
Air-hardening cast steels are used in wear applications because of high hardness, excellent abrasive wear resistance and acceptable impact toughness properties. Moreover, an air-hardening cast steel can be used in the as-cast condition without the neccessity of subsequent heat treatment. Typical alloying elements known to enhance the mechanical properties of steel are chromium, carbon, manganese, molybdenum, nickel and silicon.
Manganese, chromium, molybdenum and nickel, separately or in combination, are known to have the effect of increasing hardenability. Nickel is also known to improve impact toughness. Silicon is known to effect deoxidation and improve fluidity of a molten steel thereby enhancing castability. Silicon in combination with manganese can also have the effect of increasing hardenability.
Conventional air-hardening steels contain approximately 3-6 weight percent nickel or approximately 5-12 weight percent chromium and lesser amounts of other alloying elements. Although the addition of various alloying elements in specified amounts affects the properties of the steel, it will be appreciated that the various alloying elements, and in particular nickel and/or chromium, represent a substantial contribution to the overall cost of the steel.
Accordingly, it is an object of the present invention to utilize lower percentages of nickel and/or chromium and yet maintain optimum mechanical properties in the steel. Another object of the present invention is to provide an air hardened cast steel having a carbon level of about 0.28-0.35 w/o (as used herein w/o is defined as weight percent) and having a minimal or reduced nickel content that exhibits hardness and impact toughness properties equivalent to a steel containing approximately 4 w/o nickel, 1.4 w/o chromium, 0.25 w/o molybdenum, 1 w/o silicon and 0.30-0.35 w/o carbon. Yet another object of the present invention is to provide an air-hardening cast steel having less than 4 w/o nickel that possesses hardness and impact toughness properties substantially equivalent to a steel containing approximately 4 w/o nickel.